Avalanche forecast

Flathead Range & Glacier NP

Flathead Avalanche Center
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Avalanche danger

Tue
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Avoid steep, mid-elevation slopes above terrain traps, where you can trigger wet, loose snow avalanches with serious consequences. It also remains possible to trigger dangerous hard slabs that fail several feet deep. While the distribution of this hazard is unclear, it appears most acute on steep slopes that face northeast to southeast to southwest at all elevations. 

Avalanche problems

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Triggering loose avalanches of wet snow remains possible on very steep slopes. Rollerballs fanning out from your skis or machine are a clear sign that this hazard exists. Debris from these slides will be dense and hard to escape, so getting caught and carried in one of these slides can have surprisingly serious consequences.

    The most straightforward way to manage this hazard is to avoid riding on very steep slopes above terrain traps; with our low-tide snowpack, this includes tree wells and patches of alder and brush. This hazard is likely isolated at low elevations, where entrenched cold air has limited the warming of the near-surface snow. 

    (1/20/2024)

    Rollerballs were observed in the moist surface snow on Saturday in Kimmerly Basin. These are precursors to a wet loose slide.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3

    On many slopes, you can find persistent weak layers buried two to four feet or more deep. Although this problem has been quiet for the past few days, the seriousness of triggering a hard slab slide remains a lingering concern. At this time, there is uncertainty about the distribution of the weak layers; some layers formed in December and some at the base of our snowpack. Most seem to involve faceted snow near a melt-freeze crust buried just before the holidays (12/22). 

    Use conservative terrain management. You may or may not get cracking or collapsing before triggering an avalanche. These slides may be triggered remotely, from gentler terrain below, above, or to the sides of steep slopes. Persistent Slab avalanches can break wider and higher on slopes than expected. The only way to identify this problem is to dig into the snow. Look for faceted “sugar” snow resting above or below a crust- or at the base of the snowpack. 

    (1/18/2024)

    The crown of this avalanche was noticably deeper than other avalanches that failed in similar terrain. 

    Photo: Cam Johnson

Avalanche Discussion

Driving home yesterday (Sunday) evening, it was 27 degrees and raining near Eureka. Near Stryker, it was 30 degrees and snowing. "Welcome to our upside-down world," remarked one of my climbing partners. "Colder means snow, warmer means rain, high means warm, and low means cold." 

Indeed, it is an inverted world, thanks to warm Pacific air overrunning the cold air entrenched in the valleys after our bitterly cold Arctic outbreak last week. That's made for some complicated conditions and a low confidence in today's forecast. My immediate uncertainty is the elevation range for the Loose Wet snow avalanche problem. It seems like the upper boundary of the above-freezing temperatures Sunday was between 6000 and 6500 feet, with the lower limit about 4500 feet. Valley temperatures flirted with freezing but mostly stayed colder. Many locations saw rain. It appears only the snow surface is wet there. My conclusion is that the possibility of triggering wet loose snow avalanches is more widespread at mid-elevations, though you may find exceptions at low elevations. 

A larger, more long-term uncertainty is the distribution of the lingering Persistent Slab avalanche problem. My best guess is that mid-elevation slopes in roughly the eastern half of the compass (NE-SE-SW) harbor the most well-developed Persistent Slab structure. And that this hazard is most widespread in the southeast corner of the forecast region. It's also present in the southern Whitefish Range. Elsewhere, it appears isolated. We don't, however, have many reports from upper-elevation terrain due to difficult travel conditions. So we can't write off this elevation band or colder aspects. 

What to do with this uncertainty? Test before committing to steep slopes. These tests can take many forms. My go-to's are slope-cutting small slopes with minimal consequences and conducting small and large column tests in a snow profile. Cam and Rob's video from last week shows how to do this on a snowmachine. For column tests, I'm looking for collapses or propagation in soft layers of facets near crusts. These will be mid-pack at mid and upper elevations and near the ground lower. Propagation and collapses indicate a Persistent Slab structure is present, and that's the key info, not the score. 

Here's the rationale for my guess about distribution: Over the past week, people have reported a series of small to large natural avalanches failing near the ground, on weak, faceted snow near a crust, many on northeast aspects. While we've had reports of audible collapses from all three zones, these have been most common in the southeastern corner of the forecast region, between Essex and Marias Pass (Essex area, JFS Canyon, Skyland/Challenge area). The snowpack was shallowest in this region prior to January's storms. Last week's storms seem to have produced several large to very large natural hard slab avalanches in the Flathead Range; near Snowslip and in JFS Canyon, these look to have failed midpack, below the storm snow, at 6500 feet or above.

Regions covered